Amplifier of alternating currents



July 18, 1933. w. 'H. T. HOLDEN AMPLIFIER OF ALTERNATING GURRENTS Filed Aug. 22, 1931 INVENTOR WZflZZden/ BY f %e ATTORNEY wimmivi Enemy TownE nonnnis'rj or Bmsonwinewyom; Assxenonlro'nn nnrmn Patented July 1 ,193] i r i l.

misrinrrronn m inrir'ooiurnnxn' conron'nrronon unw; oR l lnrirnrr rnnfon nrirnnnnmrne-cunnnn'rs -This invention relates-Ito, amplifiers of empiine i an Widefrequencyband. "-Itsobject isv to prodimmer-1i networks of .cei'taiirtypes.

which the capac ties withinzithe amplifying "dune. an :unplifier, particularly for high fre" quency ivhich will treat all-frequencies with in certain working limits in the same Way;

Another specific object, is thatoi' neutralizing thevefl ect of the cepacitiesbetWeen the eleto do thisinamanner which makes the. impliiier independent oi? capacities to i ground.

E'High frequency amplifiers have been built "oiftwo types, tuned to amplify a single ire-- y 'L in p'arall'el Withfwresistaiice R51 *It uenc or a nurrowmband and untuned to m'plit'y Wide bands. ieilnlly been as sat hebrozidcasting range, and their use is timely infrequent: in present practice. Ylzirgelyh'eceuse of the shunting efiect i.tei-eiec'trecl e capacity of'the Nacuum Ktlie higher frequencies. 1; come these effects and thus accom- "tijibe beeom'e a Portion of more EXtGIlSiVQLI16twork, preferably "of the; band, pass type; of filter, thelpess band filter covering that por-l tion "of the frequency spectrum wh chntiis desired touse.

The invention will be better understood by reference to the z'followingspecification and the accompanying drawing, inwhich Figure; 1 shows the appiicetion of my invention in simple form; Fig. '2" shows al modification' thereof in which, for the'sa ke of symmetry,

t a balanced push-pull vacuum itube amplifier circuit is, used; Figsrg end l are'circuit dia grams which are to -be used inthe explanation of Figs. 1 and 2, respectl-velyyElgzfi shows afurther elaborationof my inyention tonf three-stage amplifier; and E gs j6 to 10v are schematic diegram'suseful in connection with thejexplanation of the circuit of F g. 5.

Referring toi liig. 1, there ere shown portions of a two-stage" amplifieril essential compi'ising'the' i The 5 I ternating current- ,output circuit of 3 the being connected tot-the input circuit of the 5 I tube Bthrough a network whichyes will np peer later, is one section of "ladderityp to filament isfthe inductance L with the'co ments inn vacuum tube! Still another obdenser G oflarge; capacity serving as a I helatter type has not -factory i'for frequencles :to the first nductance L; and isr'e'pi" rtheobje'ctsof my invention in part I v I U y W tlon of network: ofthella'dder type commonly using,empliiier circuitserrzmgementsja should be ofsuit'eble different valuesor' the ing in parallel f'with one oi the "induc a nces output ofjthe tube shown asfsuppliedfi 1' 4 i I withvoltagefthroughthe choke CQilLmLthenI- filter. Appearing {directly across F i r blocking condenser for direct currentkf jAl's i connected to the plate of A andezit ending' directly to the grld of Bus a'circuit conslstingnern'ss the grid circuitis a second iiidii a rice to theseeond inductance fL fand 'is 'rep reseh used in wayeffilters and shown rmoreclearl of the induetencesjL nndL jand condenser this filter section may be adiiptedfto haVef-a f pass bend in any] region off the frequ'enc spectrum desired and over this/band; there will be no attenuation. 'If the,caipacities ctJ and C 1ere"not equ'alto,each othergit nit 1 5 Will bedesirable that the twoinductencesifi difference may be compensated L3, say? the first one, a condenser C 3; which condenser in p arztllel withthe capacity'c v yieldse capacity iequelt'o 1C; ln the'event I that "t e-cgpicityfc i less than t e T. ite; t e; tyfgz 1b 11d i e dl ke i. parallelM- ith G, "Uri dertlies e cir'cumstencesl f there will' b e noette nuat ion'offtlie higli frei i grid; Qfih f eqv i er m I transmitted lies within the transmission "band of the filter section thus shown.

the output of the second tube."

.The circuit of Fig. 1 is for illustrative purposes only,iand for simplicity has been shown as connected between twostages of'amplifier tubes. Obviously, a similar" filter, preferably correspondingito a h alfsection, should beiinserted in the input of the firsttube and A filter of-the 'type'descr'ibed for its proper functioning be terminated a" load the impedance of which is equal to the impedance of the section itself. Thus the plate circuit of the tube A has a certain OllllllC' resistance and the .valuesof the inductances and capacities of thefilterisection would in general be chosen ofsuch value as to have a. characteristic impedance equal to that of the plat'ecircuit of the tube A'at thesame time as they cover the 'bandof frequencies to be transmitted. Similarly acrossthe output of thefilter'sectioii there should be aload of this same characteristicimpedance, andthis.

is provided'by a resistance R; of the appro-' priate value. Under these circumstances there will be no echo or reflection effects withinthe circuit.

A a further illustration ofmy invention, reference may be made to F1g. 2, in which thesame principles are applied to a pushpullflcircuit." Here again, the amplifiers A and B are connected in tandem, each. stage 7 beingpush-pull, and there is shown 95 a coupling between the twostages a networkanalogo us to that of Fig. 1. wB battery'in this case is applied to the platesofthe first ami pli-fier through the inductances L one for v each sideof a push-pull;circuit.- The capacities from filament to plate of each of these tubes is shown in dotted lines by C and the capacities from filament. to grid {of the amplifier- B- are similarly shown iii-dotted lines 1 by the condensers C. .In a manner similar to that of Fig.- liseries condenserC andin- "ductance-L are connected from plates of" amplifier A to grids-of amplifier. Bqandin '7 ductances L are connected across the input that'this Fig. 2 comprises two stages of am plifi'cation couple'd together by meansor' one 1 section of a1 ladder-type filter, such filter sec tion being shown for. simplificationfin 4. Q :jIt will be observed that this. section is a f. the midpoints of the shunt elements in a ma ,ner. necessary for the proper operation of the symmetricalone, making it possible to. ground plates of this amplifier A; are connected tubes and yet in a manner which do'es not interfere with the operation ofithe network as afilter section. I

As described-in connectionwith Fig. 1, it

is desirable that'the filter section :shall be. terminated in-a load whos'ejimpeda'nce is matchedwith that of the filter section. This I is accomplished through the'resistance R 'Which I is given the such matching. 1

3 appropriate 'value for "In this Fig. 2 there isshownin each aIn-' plifier a condenser OS from the grid of each tube to the plate of theother tube, this being an old and useful expedient to neutralize the tendency" of these amplifiers to. sing. e A. further modification and apre'ferred form of my invention is illustrated in F ig.-5 which shows three stages of'amplification,

each stage being.'pusl1-pull, the first. two stages beingof the typeof tube'known as screen grid tubes and the filter sections being V .of-the' form known as thejlattice type. An.

incoming linefF is connected by means .of transformer T tothe input terminals ofthepush-pull amplifiers A, there being a, filter section of the lattice typeconnected between the transformer andthe amplifier, and the details of whichwill be described later. The

through choke coils L -to positive of B'battery, and the screen grids are connected directly to a positive point on the B battery with a bypass condenser C to ground. The output of the amplifier A is'jconnecte'd through blocking condensers C and a filter section to the inputof a similar amplifierB,

, and-the outputof this amplifier is connected throughblocking condensers G and a filter section to the input of the amplifier: D, this amplifier beingshown as of the usual threeelement type, and is of a form adapted to de-- connections therefor being similar to that shownfor the amplifiers of Fig. 2. The outpu't ofthe amplifier D is supplied through a liver a substantial. amount of power, the

filter section and transformer to outgoingline H.

A better understanding of this invention 1 'will be had by reference to Figs." 6 to 10 which-may be used for deriving the relationships and characteristics peculiar to thelatg ticev type network. Thus a lattice type network of-the form shown in Fig. 6 hasan iterative impedance given by and japropagation constant given by In case Z a nd'Z are ofp oppo'site signs,as

, will in general be true forcertain frequencies i or ranges of frequencies, then the. filter is a' bandpass, filter over'that region. On the lIlG other hand, if Z and Z are of'the {same sign,

' then the filterforsuch frequencies is aastop minals 3 and lshallbe connectedto animpedance R yequal to thefiter'ativeimpedance ofthe network.

Let usnow consider the networkof Fig. 7 I wh'ich-difl'ersfrom- Fig? 6 in that each branch: of the latticenetwork has been shunted by' I i e q I q a and theziterativefiinpedance is given by y j q an impedance Z the usual :cir-cuital theorems it ,canreadily be shown that the impedance atl and2gwhen 3 and 4:are short I k n r It w illibefnotedfthat the'filte'r section-of. 3 theftypeof Fig.9."occurs beforeand aftereach amplifierstage in Fig; 5, thus;giving amfilter] i of four sections with-,certain amplification between the va'riou'sstages. .Th roug ao ltFig. f 5 C5 is-u'sed toindicate alblocking condenser v whiching'general,would'be-sufficiently large I sothat itsimpedance'for the-frequency tobe: amplified-is negligible. ltj willbe.noted, also,

that in output ofeach amplifier there is a I choke Lg, tliis'being. an. inductanceof sufli crent magnitude to} offer "substantially infinlte. impedanceto the alternating lcurrents to f be amplifiedlanid yeryllowpi npedanc tqd'i s e. l

and the impedance at 1 and2 with 3 and f Lotus now consider the circuit ofFig. 8

'WlllCll is similar to F ig.x6, except that impe'dances Z have been bridged across the terminals l and 2 and across the terminals 3 and 4.. It will be found that the impedance at 1 and 2] with 3 andil short-circuited is identically the same as for the correspond ing case of Fig. 7. Also it will be "found that the impedance at land 2 with 3 and 4; open is identicallythe same aslfthat for the cor responding case for F ig, 7. 7 networks 7 and 8 are electrically equivalent to each other. These results may be applied more specifically now to Fig. .5by referring" to Figs. Qand 10. In Fig.9 thereisshown, "a network which is similar to that encoum tered in Fig. 5 at the input of the amplifier A and terminating. in ,the resistance R of proper magnitude. L It will beg n oted that circuitof Fig. 9 is similar. tothat ofjFig. S, the impedance Z, beingreplaced the; two

condensers C in series or thetwo condensers C in series."Furthermore, ust as thef c n- :cuitofiFig. 7 may be derived from the cir'- cuit of Fig. 8, sothe circ'uit of Fig. 10 may. "be derived from the circuit of Fig. 9; Such r derivation consists in shunting the induc 'tances L and L of Fig. 9 by capacities equal to C it being understood that the capacities C 'and G are equal to eachothen'this The. usual design formulae applicable to the lat having been provided for in Fig; 5.

ticetype network maynow be applied to Fig. 10 with the assurance that they apply equally well to the circuit of F ig. 9. Such formulae to 'Masoinserial No.489,2 69, filed October may be found in various treatises on thesub- .ject of wave filters, as inan article'by (in-A.

Campbell in Bell System Technical Journal, Vol. I, No.2, pages 1 to 64, or in application 111930. a i Reference to theabove will show thatthe Therefore the M capacity" of the amplifier.

equal ty can, however, ireadily bs/adjusted the design formulae formation from the standard type to the type I understood, ;how{ l frequency;to fi lwhere amplifiers. Alan d Bfit will-notoccur'inv gen? e al that the c apaoity, from pl te andpscreen'w qual tothe input F 1 grid toflthe filament will be B. Any lack of o g's pple n l d .n'sfers such as: o...

If the, circumstances are 'such' tha'tthe input smallerthahk'the capacity of amplifier output capacity of then, of, course, the sup plemental f condensers should be associated filter of waseases-d: filter f roin'tlie" i Gleam i; beadii s ed tej li capac y 2 m s milarly, nr the last. section, thev condenser 1s ad usted to thefcapacity- C In the" y, a p 97105 second: filter, however, placed (between the;

witl zthe inputofthe amplifier B, It is w by understood thats imilar adju"s.1 :ments 'Emaycbe' I, made in, any of the 'othen filtersv if I I have-describedindetail the aser section and-prefer this arises.

lattice type of filter form because of'the'relative simplicitvof I shown in Fig.5. It is to be ever, that my invention is not limited to suchfilters but that these may V 1 r of which one illustration {is givengin -Figs.

1-and'2. j

Whatisclaimed is: 1

involved and the trans-1 take on any form, i

1.IA-vac1 ium tube amplifying 'cirouitdf ivz amplifying frequencies over agiven -band-,"" v

combination, and a filter associated wallow-11?? comprls ngtwo tubesiassociated in push-pull pair of. terminals thereof and adapted to pass the desired frequency baiid, the capacities of the tubes as seen from said terminals being elements in the filter;

2. A vacuum tube amplifier circuit for amplifying frequencies Over a given band, comprising two tubes associated in push-pull- :combination, and a lattice type filter vin the input circuit with theinput capacities of the tubes as elements thereof and Wlth'itddltlOIlfil elements to compensate'tlierefor.

3. A vacuum tube amplifier circuit for amplifying frequenciesovera given band,

i i comprising two tubes associated in push-pull combination, and a lattice type filter in the output circuit with the output capacities, of

the tubes as elements thereof and .With additionaleleme -its to compensate therefor.

A. A; vacuum tube amplifier circuit for amplifying frequencies over a g ven band,

- comprising a plurality of stages of'amplification, each stage comprising two tubes associated in push-pullcombination, and a lat prising a vacuum tube and a filter associated I with the input circuit andv adjusted to pass the desired frequency band, theinput cas tice type filter between any tWo stages there,-

v of, the internal capacities of the output terinirials of one stage. and the internal capacities of the input terminals of the next stage being elements in the filter, these With other elements making the filter a pass band filter over the given band.' i

5. -Avacuum tube amplifier circuit for: am

pli fying frequencies over a given band,'compacity of the tube being an element in the filter a resistance across the input circuit of such value as to substantially match the characteristic impedance of the filter. j

j 6. A vacuum tube amplifier circuit for areplifyin'g frequencies over a given band, comprising a vacuum tube and a filter associated \vitlithe output and'adjuste'd to pass the de sired frequency band, the output capacity of the, tube beingan element inthe filter, the

values of the elements in the filter'being such that the characteristic impedance of thefilter is'equal to the internal impedance of the tube 7 across itsoutput terminals:

v to thetube;

8. Avacuuin tube amplifier circuit for ainplifying frequencies over a given band, comprising tWo stages or vacuunitube V amplifiers and a filter connected between the two stages, the internal capacity f the output t'erminals'of the first stage and the internal capacity of the input terminals of the second stage beiiigelemcnts in the filter,-tliese ele- 5' ments With others making the filter tbLIlCll pass filter over the giveiirange, the characteristic impedance of-the filter bein'g made equal to the output in'ipedance'ofthe firsttube,

'9. The combination of claim 8 character: ized by a,resistance across thegrid ofv the second tube of such valuethat the filter is terminated in its characteristic impedance.

'10. The combination ofclaim 8 characterized by a supplemental condenser in the] filter to equalize tbeinternal capacities of the outputjof the first-tube and the'inputof the sec ond tube, and further characterized by a resistance across the grid of the second tube ofj'su ch value that thev'filter is terminated' in its characteristic impedance.

11. A vacuuii' tube amplifier circuit for amplifying frequencies over a given band,

COHIPLiSlIlg' a screen grid-vacuum tube amplifier, a filter associated with theoutput circuit thereof and adjusted to pass the desired frequency band, the capacity of the plate and the'screen grid being an element in the filter.

12. The combination of claim 1 characterized by the fact that the filter isof the 'sym-' metrical type With midpoints ofthe 'shunt elements grounded.

WILLIAM T; iioLDENf, 

